In view of the actuality that the surface ship can’t exactly recognize the type of incoming torpedo in defense action,fourteen indices correlating to recognize torpedo types are extracted and sorted in acquirable difficulty.In view of some deficiencies in Dempster-Shafer theory,a sort of improved data fusion algorithm is established.A pretreatment method for certainty information is introduced,and the entire flow chart of information fusion is designed.The simulation result proves the algorithm here is more accurate than the traditional method.It can ensure surface ship take action exactly to defend against incoming torpedos.